Manufacture of alpha cellulose



"\ l 4 i i I l I i a o m Li J. S. POU

v MANUFACTURE OF ALPHA CELLULOSE Filed Febf23, 1934 April 9, 1935.

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Patented A r. s, 1935 PA-TENT ol-F cE MANUFACTURE OF ALPHA CELLULOSE,

Jose Sala Pou, Barcelona, Spain Application 3 Claims.

I have filed an application in Spain on the 21st October, 1933.

4 The present invention relates to the manufacture of alpha cellulose,andmore particularly to 5 a process for manufacturing this product frombamboo canes in a form suitable for the production of cellulose estersas substitutes for cotton pulp and its derivatives. 7

The plants of the order Graminacete, species -of'bamb'oos', have fibrespossessing special characteristics, a fact which has already been knownto paper manufacturers; but the said fibres have.

not hitherto been used for the manufacture of super-alpha cellulosescapable of competing in the market with the super-alpha cellulosesderived from cotton.

The nature of the plants, which are different in their constitution fromwood, leads to the assump: -tion of the possibility of the formation ofa cellulosic compound which being less lignified, may givecharacteristics more similar 'to the polymerization ofthe cottonmolecule. On the otherhand, the greater percentage of lignine which theplants contain ascompared to the other plants of the order Graminaceae,allows also ofthe bamboos producing a cellulose in the form of'filaments having fibro-vascular fascicles of a bleaching chlorine andwhich can be with difficulty eliminated by the latter unless thechlorine is used in proportions which always produce considerableoxidation ofthe fibres. Moreover, the peptins can be easily renderedsoluble by alkaline hydrates at temperatures in the neighbourhoodv ofdegrees.

In view of the simplicity with which the peptins are eliminated theideahas been conceived to use in place of a continuousprocess, a fractionalprocess which at a first boiling at a presv sure of 0.5 atmosphere in analkaline lye containing 1.5 per cent of the corresponding alkali, in theproportion of 1 :5 between the weight of the material treated and theweight of the bath, elim- February23, 1934, Serial No. 712,628 In-SpainOctober 21, .1933

inates the peptins; This quantity of hydrate is sufiicient forconverting them into the form of a soluble salt which remains insolution. The combination of sugars, starches and peptins formed, owingto the excess of alkali which remains in the bath without reacting,cannot be abstracted, as otherwise it would be precipitated and wouldstain the cellulose fibre to such an extent that-it would be difiicultto clean it.

The alkaline hydrates, even at the low temperal tures at which theoperation is carried out, always exerta hydrolyzing effect on thehemi-celluloses which accompany the alpha cellulose, and the oxidizingmolecules of-the hydrates always exercise some hydrolytic action' alsoon the alpha i celluloses. For that reason it has been consideredadvisable to introducein the first stage a reducing element such as-analkaline sulphite or sulphites, which combining with-oxygen, preventsthe said hydrolyzing effect andleaves the elimi- 2 nation of the lignineand of the semi-celluloses to the second stage of the process, so thatthe first stage thereof serves only for the elimination of theabove-mentioned substances.

The combined'action of the alkaline hydrates 2 and of the alkalinesulphites must take place at the temperature and pressure indicated andwithin a period of time of two to four hours. As soon as this firststage of the operation is completed, the pulp is washed first with hotwater and then a two or three times with cold water. Into the autoclavein which the operation is carried out, anew lye which contains per litre45 grammes of alkaline hydrate, 20 grammes of sulphide of sodium and 5grammes of sulphite of sodium is 3 then introduced.

The first object aimed at by the use of this lye is to avoid theeifectsof hydrolyzation which have been provided for in the first stage.Sodiumsulphide and sulphite are intended to attain this 4 object. Forthe same purpose the lye in the form of sodium sulphide and causticsoda, could also be-combined in any proportion which may be con-'sidered suitable for combining the said products with the lignine. 4The highly beneficial reducing effect of the sodium sulphide forobtaining super-alphas may be assumed'to' be represented by thefollowing equation:

NazS+HzO=NarS+HOH=NaOH1=NaHS This reaction, which, as indicated isreversible, is a. hydrolysis which gives sodium sulphohydrate, and thisproduct forms the reducing atmosphere 6 which prevents the effect ofoxidation on the alpha cellulose. I

The acid contents of the lignine or the lignitic acids are neutralizedby the alkaline hydrate or by the hydrolysis of the NazS to NaOH, givingsoluble soda compounds.

The NaHS combines with alcohols (to form mercaptans) and with phenols,the result of the reaction being by weight, with regard to the sulphide,as follows:

i Per cent Combined with the lignine after the hydrolysis 51.8 Retainedby volatile organic substances 15.0 Remaining unaltered as NazS 15.8Eliminated in the form of sulphate 17.8

This oxidation of sulphide in order to pass to sulphate takes place atthe expense of active oxygen which would have produced oxidizing actionon the alpha celluioses.

The temperatures applied for the elimination of the lignine start at 140degrees C., but in some kinds of old bamboos, that is to say, bambooswhich arein the advanced period of lignification, or inthe bamboos whichgrow in shallow soils which prevent the roots of the plant frompenetrating deeply into the earth and where the rainy periods areveryrare or the'rain is scarce between the stage of first growth of thestem and the stage of second growth in which latter the branches and theleaves appear, asa result of ,which there is a lack of moisture in theroots and therefore in the plant, with the consequent quick drying up ofthe starches in the fundamental porenchyma of the plant, on the saidalimentary substances being eliminated for the normal development of thecellulose until its maximum uniform growth is reached, there takes placea premature ageing, so

that a premature kind of very much condensed lignine is produced whichstrongly envelops the fibres in the ligneous fibro-vascular sheafs orfaggots, and which is difiicult to eliminate by the industrial processesfor the elimination of the said product, and in such cases it isnecessary to use high temperatures of degrees C. which produce on theother hand a serious hydrolysis of the alpha cellulose.

In spite of the reducing atmosphere which the sulphide produces, it hasbeen found difficult to avoid these actions, and in order to avoid alsosuch high temperatures, and it has been attempted to find some solventfor the lignine. A' suitable solvent has been finally found among theethers of the phenols. As an example of this solvent, may be usedguayacol, that is to say monomethyl ether of the phenol which is foundin cellulose. The guayacol quickly dissolves the coating of ligninegelatinized by the hydrate and allows new portions of the lye to attackrapidly new zones of lignine. Owing to the action of the guayacol it ispossible, even in cases where old.

bamboos or bamboos'grown in bad conditions are used, to do withoutvarying the times and the pressures required for the operation, and inthese pressure of 8 atmospheres.

After the completion of the boiling, a. further washing operation withhot water is carried out. When guayacol has been used, the first wateris emulsified with a benzol in the proportion to the quantity of theguayacol used, plus 50% by weight of this body. .After twice washingwith hot water, the product is washed two or three times with coldwater, and thereupon bleached with a hypochlorite solution of one halfto one degree B. This cellulose thus obtained is washed and submitted tothe action of a HFl bath of half percent. In this way the remains of thesilica are eliminated, and the residue of ashes can be reduced to 0.3%.After this bath, the product is washed in plenty of water, and thebleached cellulose is subjected to the action of a solution ofbisulphite of soda of 2 B. at a temperature which may vary between 60degrees C. at atmospheric pressure and '120 degrees C. at a pressure ofone atmosphere. This operation eliminates the quantities of oxiandhydrocellulose, and the rest of the lignine that may still be left.After this bath, the cellulose is washed in plenty of water and may besubmitted if desired to the action of'a solution of peroxide of sodiumor of peroxide of hydrogen for the purpose of improving its whiteness.

The cellulose obtained by this process from the bamboos has exceptionalcharacteristics which are in no way inferior to the characteristics ofcotton.

For carrying out the reactions and operations above set forth it ispreferred to employ an installation comprising a combination ofelements, by means of which the whole process according to the inventioncan be carried out automatically from the commencement up to thedelivery of the cellulose without the necessity for manual operations.

A preferred constructional arrangement of such an installation isillustrated by way of example in the only figure .of the accompanyingdrawing.

Referring to the drawing:

The cut bamboos afterhaving been left to dry in the field for a periodof forty days, are exposed to the action of running water, either in ariver or in suitable pools for a period of time which varies from 7 to15 days.

The bamboos prepared in this way are introduced into a grinding mill lconstituted by four pairs of cylinders or rollers, two of which areprovided with grooves or flutes, and these two rollers owing to theaction of hydraulic pressure applied to them, flatten and break thejoints or knots of the bamboos. The other two pairs of rollers areprovided with teeth arranged in zigzag shape and are also subjected tostrong by draulic pressure, their object being to cut the bamboos. Thisoperation is of the greatest importance, inasmuch as, the uniformity ofthe boiling depends on the elimination of the air from the perforatedvessels, since the said air may cause the mass to fioatin the boilinglye, which would retard by at least one hour the time of immersion.

The bamboo stems having been cut to portions of about one squarecentimetre section and completely disintegrated, drop into a pit whichis 10- cated in front of buckets 2 which lift the cut stems up to thehopper 3. The said hopper is so dimensioned that its capacity is thesame as that of the autoclave 4 with which it is associated. The saidautoclave receives the new lye which is supplied from 18, and which hasbeen mixed in a well ill provided with an agitator, with the regeneratediyes coming from the tank 26.

As soon as the cut bambro and the lye have been introduced in the saidmanner into the autoclave, steam is admitted from a steam generator 20the said steam being used. for indirect heating so as to avoid anydilution of the bath. This point, though it is not of much importance inthe production of cellulose intended for the manufacture of paper, isimportant in the case of those super-alpha celluloses in whichvariations to the extent of one tenth percent in the lye are liable toproduce variations of more than two percent in the contents of thealpha. At the proper moment, the top valve of the apparatus is opened,and a circulating pump with which it is provided, is started, for thepurpose of enabling the air contained in the mass consisting of lye andbamboo tobe expelled. This operation is of great importance as it avoidsthe oxidation of the cellulose by the oxygen of the air. As soon as thisoperation is finished, the temperature is raised until the pressurepreviously stated is reached and is maintained during the period of timealso stated, whereupon the lye is discharged through a valve and sentfor recovery or recuperation. The mass contained in the autoclave, isthereupon washed once with hot water and three times withcold water.

This first stage of boiling of the bamboo being finished, the lye bymeans of which the second operation or stage is carried out, isintroduced into the autoclave, the same precautions being taken withregard to the air as were adopted in the previous operation, and acontinuous circulation being kept up during theboiling operationby meansof the pump already referred to.

As soon as the operation is finished and after the washing operationswhich follow those with emulsioned benzol, the lye is returned to thewell 5 from which it passes together with the first two washing waters,to a tank 2| serving for the reception of the lyes which are to betreated for recovery or recuperation.

The lyes from the tank 2| are conveyed to a. multiple action evaporator22 which is fed with the steam coming from the steam generator 20 andvafterwards pass to the rotary oven 23 in which they are calcined andfrom the latter pass to thekpit 24 from which an Archimedean screwraises them to the caustifying vessels 25. from which they pass tosettling tanks 26.

As soon. as the lyes have been conveyed to the recovery units, thecellulose is returned to the well 5 in which it is diluted with waterand washed therewith, being stirred for the purpose by a powerfulagitating device. The pulp which is thus formed, is conveyed by means ofa pump to a thickener or concentrator 6 which in its turn after havingeliminated the water, delivers the pulp to a disintegrator-deflbrator ofthe kind known under the name of cone breaker. This disintegrator issufiicient for the purpose in asmuch as the material to be treated isthoroughly boiled pulp which does not normally contain any knots (sinceit has been ground in the mill I); but in cases in which, owing to somedefect in the grinding mill, the knots of the bamboos had not alreadybeen sufliciently ground, it would be necessary to interpose between thewell 5 and the concentrator 6, one or more rotary purifiers working withone millimetre pitch.

On being discharged from the cone breaker, the pulp is introduced intoone or more washing and bleaching vats or machines 8 to which issupplied a solution of sodium hypochlorites supplied from decantingdevices 30. From the said washing and bleaching machine or machines 8the cellulose passes to a vat 9 where it is treated with hydrofluoricacid of the above-mentioned concentration. This vat is lined inside witha plastic material having for its basis rubber, in order to render itproof against the action of the acid which comes from a supply unit 29.

The cellulose passes from the vat I to a vat III in which it is washedwith plenty of water until the last traces of the acid are removed andfrom the said vat the cellulose passes to a concentrator II from whichit is here conveyed by a pump into an autoclave l2.

The cellulose is introduced into the autoclave l2 through the bottompart of the latterand is forced to circulate through several inclinedplanes arranged in the interior of the said autoclave, arid at theproper time the corresponding solution of sodium sulphlte is introduced.The bath is thereupon heated by means of steam coming from the steamgenerator 20 and passing through a closed coil arranged at the bottom ofthe apparatus. In these conditions, the pressure rises to oneatmosphere, and the pulp is extracted from the upper part of theautoclave by a pump provided with a special pressure-relief device. Onits discharge from the said pump, the pulp passes into a vat I3 in whichit is thoroughly washed. The sulphlte used in the last named lye issupplied from a unit 21.

The pulp contained in the vat l3, after having been treated in thelatter, passes to the vat I where it is treated with a solution which isprepared in a unit 28-and which is composed of sodium peroxides orhydrogen peroxides, and on leaving the vat M, the pulp passes through along sand-removing device l5, from the latter to a centrifugal purifierl5 and finally to a pulp press i1.

The pulp thus obtained which contains from 97 to 98% of alpha celluloseis of a magnificent white colour, and its fibres are 7 to 8 millimetreslong. This super-alpha cellulose with such exceptional characteristics,extracted from bamboos, is obtained in a proportion of 35 to 40% of thedry 'plant and is more particularly suitable for the esterification aswell as for the manufacture of papers, particularly of papers fordocuments, ledgers and bank notes. Moreover in view of the exceptionalabsorption capacity which this fibre possesses, it can be used in placeof cotton for the hygienic and sanitary purposes for which the latter isemployed.

The product obtained by the process hereinbefore described, has thefollowing characteristics:

Viscosity equal to that of pure normal cotton in a cupro-ammoniacalsolution of 0.5%

, subsequent use may also vary and generally the process, installationand product may be modified in various ways without departing from thescope of the invention.

I claim:

1. A process for the manufacture of alpha cellulose from bamboos,comprising in steps: drying out bamboo in the open air; exposing the cutand dried bamboo to the action of running water; grinding said bamboo toform a kind of tow; boiling said tow in an autoclave with a lye composedof alkaline hydrates and a reducing agent at a pressure of .5 to 1atmosphere; washing said tow in the autoclave first'with hot water andthen with cold water; subjecting the bamboo pulp thus produced in thesame autoclave to the action of a second lye containing alkalinehydrate, sodium sulphide, sodium sulphite and guayacol for one hour at156 C. and 4.8 atmospheres pressure, and for a few hours at 143 C. and 3atmospheres pressure; washing the pulp in the autoclave first with wateremulsified with benzol and then three times with cold water; dischargingthe pulp into a tank fitted with an agitator and diluting it with water;passing the pulp through a thickener and then through adisintegrator-de'fibrator; subjecting the pulp to the oxidizing actionof sodium hypochlorite lye, washing it in plenty of water and subjectingit then to the action of a bath of hydrofluoric acid and again washingwith ample water; passing the pulp through a thickener and then into anautoclave in which it is mixed with a suitable quan tity of sodiumsulphite at 60 C. and 2 atmospheres pressure and then washed; andbleaching the pulp with hydrogen peroxide or sodium peroxide, washingit, and converting it into solid form.

2. A process for the manufacture of alpha cellulose frombamboos,-comprising in steps: drying cut bambooin the open air; exposingthe cut and dried bamboo to the action of running water; grinding saidbamboo to form a kind of tow; boiling said tow in an autoclave with alye composed of alkaline hydrates and a reducing agent at a pressure of-.5 to 1 atmosphere; washing said tow in the autoclave first with hotwater and then with cold water; subjecting the bamboo pulp thus producedin the same autoclave to the action of a second lye containing alkalinehydrate, sodium sulphide, sodium sulphite and guayacol for one hour at156 C. and 4.8 atmospheres pressure, and for a few hours at 143 C. and 3atmospheres pressure; washing the pulp in the autoclave first with wateremulsified with benzol and then three times with cold water; dischargingthe pulp into a tank fitted with an agitator and diluting it with water;passing the pulp through a rotary purifier having a pitch of 1millimetre for removing any bamboo knots which have still been leftunground during the previous mechanical action to which the pulp hasbeen submitted; passing the pulp through a thickener and then through adisintegrator-defibrator; subjecting the pulp to the oxidizing action ofsodium hypochlorite lye, washing it in plenty of water and subjecting itthen to the actionof a bath of hydrofluoric acid and again washing withample water; passing the pulp through a thickener and then into anautoclave in which it is mixed with a suitable quantity of sodiumsulphite at 60 C. and 2 atmospheres pressure and then washed; andbleaching the pulp with hydrogen peroxide or sodium peroxide, washingit, and converting it into solid form;

3. A process for the manufacture of alpha cellulose from bamboos, in aform suitable for conversion to cellulose esters as substitutes forcatton pulps and derivatives comprising in steps: drying the cut bambooin the field in the open air for forty days; exposing the-cut and driedbamboo to the action of running water in a river for from"? to 15 days;grinding said bamboo to form a kind of tow; boiling said tow in aautoclave for a period of 2 to 3 hours with a circulating lye, the ratiobetween the amount of the tow and the lye being 1:5, and the lye beingcomposed of alkaline hydrates together with 1.5 to 2 percent of areducing element, the boiling operation taking place at a pressure of .5to 1 atmosphere and the temperature corresponding thereto; washing saidtow in the same autoclave first with hot water and then three times withcold water; subjecting the bamboo pulp thus produced in the sameautoclave to the action of a second lye containing per litre 45 grammesof alkaline hydrate, 20 grammes of sodium sulphide and 5 grammes ofsodium sulphite together with a suitable quantity of guayacol, the lyebeing caused to circulate through the bamboo pulp for 1 hour at 156 C.and 4.8 atmospheres pressure, and then for 2 to 3 hours at 143 C. and 3atmospheres pressure; washing the pulp in the autoclave first with wateremulsified with benzol in the proportion of one-and-a-half times theweight of the guayacol and then three times with cold water; dischargingthe pulp into a bleaching the pulp with hydrogen peroxide or sodiumperoxide, washing it, and converting it into the usual known solid form.

JOSE SALA POU.

